fix: preserve repeated blob matches in getBlobs

packages/beacon-node/src/api/impl/beacon/blocks/index.ts

@@ -68,7 +68,7 @@ import {kzg} from "../../../../util/kzg.js";
 import {promiseAllMaybeAsync} from "../../../../util/promises.js";
 import {ApiModules} from "../../types.js";
 import {assertUniqueItems} from "../../utils.js";
-import {getBlockResponse, toBeaconHeaderResponse} from "./utils.js";
+import {getBlobIndicesByVersionedHashes, getBlockResponse, toBeaconHeaderResponse} from "./utils.js";
 
 type PublishBlockOpts = ImportBlockOpts;
 
@@ -983,15 +983,7 @@ export function getBeaconBlockApi({
             const blockVersionedHashes = blobKzgCommitments.map((commitment) =>
               toHex(kzgCommitmentToVersionedHash(commitment))
             );
-            indicesToReconstruct = [];
-            for (const requestedHash of versionedHashes) {
-              const index = blockVersionedHashes.findIndex((hash) => hash === requestedHash);
-              if (index === -1) {
-                throw new ApiError(400, `Versioned hash ${requestedHash} not found in block`);
-              }
-              indicesToReconstruct.push(index);
-            }
-            indicesToReconstruct.sort((a, b) => a - b);
+            indicesToReconstruct = getBlobIndicesByVersionedHashes(blockVersionedHashes, versionedHashes);
           } else {
             indicesToReconstruct = Array.from({length: blobCount}, (_, i) => i);
           }
@@ -1022,16 +1014,9 @@ export function getBeaconBlockApi({
             toHex(kzgCommitmentToVersionedHash(commitment))
           );
 
-          const requestedIndices: number[] = [];
-          for (const requestedHash of versionedHashes) {
-            const index = blockVersionedHashes.findIndex((hash) => hash === requestedHash);
-            if (index === -1) {
-              throw new ApiError(400, `Versioned hash ${requestedHash} not found in block`);
-            }
-            requestedIndices.push(index);
-          }
+          const requestedIndices = getBlobIndicesByVersionedHashes(blockVersionedHashes, versionedHashes);
 
-          blobs = requestedIndices.sort((a, b) => a - b).map((index) => blobs[index]);
+          blobs = requestedIndices.map((index) => blobs[index]);
         }
       } else {
         blobs = [];

packages/beacon-node/src/api/impl/beacon/blocks/utils.ts

@@ -73,3 +73,29 @@ export async function getBlockResponse(
 
   return res;
 }
+
+export function getBlobIndicesByVersionedHashes(blockVersionedHashes: string[], requestedHashes: string[]): number[] {
+  const indicesByHash = new Map<string, number[]>();
+
+  for (const [index, hash] of blockVersionedHashes.entries()) {
+    const indices = indicesByHash.get(hash);
+    if (indices) {
+      indices.push(index);
+    } else {
+      indicesByHash.set(hash, [index]);
+    }
+  }
+
+  const requestedIndices: number[] = [];
+
+  for (const requestedHash of requestedHashes) {
+    const indices = indicesByHash.get(requestedHash);
+    if (!indices?.length) {
+      throw new ApiError(400, `Versioned hash ${requestedHash} not found in block`);
+    }
+
+    requestedIndices.push(...indices);
+  }
+
+  return requestedIndices;
+}

packages/beacon-node/test/unit/api/impl/beacon/blocks/utils.test.ts

@@ -0,0 +1,12 @@
+import {describe, expect, it} from "vitest";
+import {getBlobIndicesByVersionedHashes} from "../../../../../../src/api/impl/beacon/blocks/utils.js";
+
+describe("api - beacon - blocks utils", () => {
+  it("returns every matching blob index in request order", () => {
+    expect(getBlobIndicesByVersionedHashes(["0xaa", "0xbb", "0xaa", "0xcc"], ["0xbb", "0xaa"])).toEqual([1, 0, 2]);
+  });
+
+  it("throws when a requested versioned hash is missing", () => {
+    expect(() => getBlobIndicesByVersionedHashes(["0xaa"], ["0xbb"])).toThrow("Versioned hash 0xbb not found in block");
+  });
+});